The present invention relates to a mounting structure of plastic glass in a watch case.
In order to mount a plastic glass cover in a watch case, the plastic glass is deflected by a tool with the aid of jigs to a diameter smaller than the opening for the glass of the watch case. After the plastic glass is inserted into the opening of the watch case, the jigs are removed to permit the case to engage with the plastic glass in the recess of the watch case. Since the plastic glass is considerably deflected to contract its diameter, stress is produced in the glass during the mounting operation. The stress will eventually cause a crack to develop in the glass after a long period of use, which results in penetration of water and dust into the watch in addition shortens the life of the glass. If the glass is excessively deflected, a permanent set will remain in the glass resulting in a permanent deflection. Such deflection will decrease the resistivity to the penetration of water and dust and cause removal loss of the glass in an extreme case.
On the other hand, the plastic glass must be made in a spherical shape to allow for a certain amount of deflection. Therefore, it is impossible to design the plastic glass into another shape such as crystalline shape.